Computer Chip Life Cycle

Most computer chips are primarily composed of crystalline silicon. The first step, therefore, is silicon mining and purification. Among many other things, this requires energy. Energy is one of the inputs of the mining and purifying process. The output is purified silicon, which gets shipped to a computer chip factory.

The computer chip factory then takes the purified silicon and makes it into a crystal wafer form. The purified silicon is an input of the manufacturing process. Only about 43% of the pure silicon crystal used in the process becomes part of the chip. The silicon that does not end up in a chip either comes out as a recyclable output or as waste.

Of the silicon that does not end up as a part of a chip, some is used to make solar panels, and the rest is either disposed or recycled back into the system. If some "waste" is used as an input for a different process (solar panel manufacture, in this case) or is recycled, then the material is not actually wasted. This is one way industrial ecologists try to reduce waste - they identify processes that can actually use other processes' waste as an input.

Then the factory "etches" circuits on the silicon wafer and cleans the etched wafer, and places the transistors and other circuits on the chips. The inputs to these processes are, among other things, chemicals to etch the silicon and water to flush it out. For a 2-gram, 32-megabyte memory chip and its plastic package, about 70.5 pounds of water is used (Williams, et al, 2002). The water used in the process must be purified before it can be used. It is then used to wash the silicon wafers and is passed out of the system as waste, or effluent. This effluent contains the chemicals it washed off the wafers, and therefore has to be disposed according to federal and state regulations. About 0.16 pounds of chemicals are used for each 0.004 pound chip produced, which is about 40 times the weight of the chip.

Finally, the factory cuts the wafer up into the actual chips that are packaged in a form ready for assembling in other products.

Through every step of the production process, energy is required as an input. The silicon crystal that is used must be extremely pure since tiniest impurities will cause the chips to fail. Creating the absolute clean environments required to produce such pure substances is energy-intensive. It has been calculated that the equivalent of 3.5 pounds of fossil fuels are used in the production of the memory chip and its packaging, because most electricity in the U.S. is generated from fossil fuels, particularly coal. Energy is one of the most important inputs in the manufacturing process.

To get a full picture of the impact of a product's manufacture, it is necessary to follow the entire chain of inputs and outputs, upstream and downstream.

To manufacture a computer chip, we have:

1.Raw Material Extraction: inputs, outputs and processes required to produce a supply of energy and silicon, including mining of materials. 2.Material Production: inputs, outputs and processes to produce crystalline silicon, including the crystallization of purified liquid silicon. 3.Part Production: inputs, outputs and processes to manufacture a chip, including etching circuits on a silicon wafer. 4.Assembly: inputs, outputs and processes to produce the final packaged chip, including the plastic or ceramic case with metal pins that encases the chip.

This is just the beginning of the life of a computer chip. Once it is put into the electronic device and turned on, the chip consumes electricity (energy). When the device that the chip is in has outlived its usefulness, the chip is disposed of, either as waste or recycled material. This is the "disposal" phase of the chip, and is the last phase of its life cycle.

Computer chips have a high environmental impact relative to their weight. For every gram of a microchip, 630 grams of fossil fuels are used, whereas for every gram of an automobile, only 2 grams of fossil fuels are used. This is due to the fact that making very pure, organized and hence low entropy structures from high entropy materials require large energy inputs. Automobiles, while made with heavy materials, do not require the level of purity and sophistication of materials as a microchip. The energy used in producing nine or ten computers is enough to produce an automobile.

How Chips are MadeThis website, presented by Intel's Innovation in Education website, describes how computer chips are manufactured.

Wired: "Smoothing the Way to Faster Chips"This research article reports on the push to develop faster semiconductors. By altering the acidity and composition of the chemicals used to etch the chips, researchers hope to minimize the roughness of each silicon wafer's surface. The smoother the surface, the faster the chip's processing speed.

Williams, Eric, Robert Ayres, and Miriam Heller. The 1.7 Kilogram Microchip: Energy and Material Use in the Production of Semiconductor Devices. Environmental Science and Technology, 36 (24), 5504 -5510, 2002.